Method of manufacturing a liquid crystal device including a peripheral circuit area and a pixel area on the same substrate

ABSTRACT

In forming four liquid crystal panels on a glass substrate, layout is so made that peripheral driving circuit areas of the respective panels are opposed to each other. With this layout, the peripheral driving circuit areas, which are prone to be affected by particles, are prevented from existing in regions close to the perimeter of the glass substrate. This allows liquid crystal panels to be produced at a high yield, as well as enables efficient use of the glass substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method of a displaydevice having a pixel area and a peripheral driving circuit area and,more specifically, to a manufacturing method of an active matrix typeliquid crystal display device.

2. Description of the Related Art

An active matrix liquid crystal display device is conventionally known.In the active matrix liquid crystal display device, a structure is knownin which a pixel area having pixels that are arranged in a matrix formand a peripheral driving circuit for driving thin-film transistors thatare arranged in the pixel area are integrated on the same substrate.

FIG. 1 shows a general configuration of a panel of an active matrixliquid crystal display device in which a pixel area and a peripheraldriving circuit area are integrated on a glass substrate 101. Referencenumeral 102 denotes a pixel area in which pixels are arranged in amatrix of several hundred by several hundred. The fundamentalconfiguration of the pixel area 102 is such that source lines 104 andgate lines 105 are arranged in a matrix form, thin-film transistors 106are arranged at each intersection of the source and gate lines, and thedrains of the thin-film transistors 106 are connected to electrodes(pixel electrodes) for applying an electric field to a liquid crystal107.

Reference numeral 103 denotes a peripheral driving circuit area fordriving the thin-film transistors for the respective pixels. Theperipheral driving circuit area 103 is also constituted of thin-filmtransistors. The standardized configuration of the peripheral drivingcircuit includes a shift register circuit and an analog buffer circuitthat allows a low-impedance current flow.

In general, plural panels of the active matrix liquid display deviceshown in FIG. 1 are produced at the same time by forming a plurality ofFIG. 1 configurations on a large glass substrate and then cutting theglass substrate, because this method can reduce the manufacturing costfrom the case of producing the panel of FIG. 1 one by one.

FIG. 2 shows a general layout of active matrix liquid crystal displaypanels. That is, in FIG. 2, a single glass substrate 101 is allocated tofour active matrix liquid crystal display panels 201 to 204. The numberof panels to which a single glass substrate is allocated is not limitedto four, but may be set as desired.

SUMMARY OF THE INVENTION

The layout as shown in FIG. 2 can provide an advantage that themanufacturing cost of the active matrix liquid crystal display devicecan be reduced. However, it has been found that if panels are actuallyproduced with the layout as shown in FIG. 2, failures likely occur witha particular tendency.

For example, if the single glass substrate 101 is allocated to the fourpanels 201 to 204 in the manner shown in FIG. 2, failures occur at ahigh probability in the panels 201, 203 and 204. The reason is explainedas follows. It has been found that where the active matrix liquidcrystal display panel of FIG. 1 is produced singly, more than 80% ofcircuit failures occur in the peripheral driving circuit area 103.Further, observations with an optical microscope have revealed thatfailures are caused mainly by particles.

The fact that failures occur in the peripheral driving circuit area 103at a high probability attributes to two concurrent factors. First, theperipheral driving circuit area 103 has a much higher degree ofintegration than the pixel area 102. The second factor is as follows. Ingeneral, as exemplified in FIG. 9, a thin-film transistor manufacturingprocess includes many steps. For example, when a substrate is moved in atransition from one step to the next, minute particles fall on thesubstrate more likely in a region closer to the perimeter of thesubstrate.

Since the peripheral driving circuit area 103 has a higher decree ofintegration than the pixel area 102 as described above, a failure iscaused by particles at a higher probability in the peripheral drivingcircuit area 103. On the other hand, where semiconductor devices areformed on a single substrate, particles (dust) are distributed on thesubstrate in each step (in general, semiconductor devices are formedthrough many steps) at a higher percentage in a region closer to theperimeter of the substrate. Therefore, when a panel is produced as shownin FIG. 1, a failure occurs at a higher probability in the peripheraldriving circuit area 103. Once a failure occurs in the peripheraldriving circuit area 103, no signal current flows through a gate line ora source line that is connected to a location of failure, resulting in aline defect. Even if the failure does not cause a line defect, it willcause a flicker on the screen or an unclear display.

Now, where the respective cells are produced with the layout of FIG. 2,it is seen that the peripheral driving circuit areas 205, 207 and 208,which themselves are prone to a failure due to particles, exist inregions close to the perimeter of the glass substrate 101 in whichregions particles occur at a high probability. Thus, it is understoodthat failures occur at a high probability in the peripheral drivingcircuit areas 205, 207 and 208.

Based on the recognition of the foregoing problem, an object of thepresent invention is to provide a technique of suppressing failures in acase where a plurality of panels are produced from one substrate asshown in FIG. 2.

According to one aspect of the invention, there is provided a method formanufacturing a panel that constitutes a liquid crystal display devicein which a pixel area and a peripheral driving circuit area are formedin an integral manner on a substrate having a insulating surface,wherein layout is so made that a distance between the perimeter of thesubstrate and the peripheral driving circuit area is longer than adistance between the perimeter of the substrate and the pixel area.

In the above method, usually a glass substrate is employed as thesubstrate having an insulating surface. Alternatively, a quartzsubstrate or a resin substrate may also be used.

The pixel area has a number of pixels that are arranged in a matrixform. Each pixel has at least one switching thin-film transistor and, ifnecessary, a holding capacitor. The peripheral driving circuit areaincludes circuits for driving the thin-film transistors in the pixelarea. The peripheral driving circuit may includes thin film transistorsformed on the same substrate as the switching transistors.

FIG. 7 shows a specific example of the feature "layout is so made that adistance between the perimeter of the substrate and the peripheraldriving circuit area is longer than a distance between the perimeter ofthe substrate and the pixel area." The example of FIG. 7 is directed toa case of producing four panels from a glass substrate 101. In thiscase, distances a and b between the perimeter of the glass substrate 101and a peripheral driving circuit area 701 are set larger than distancesa' and b'. A similar layout may be used for a case where the number ofpanels produced from a single substrate is larger than four. Inaccordance with a preferred embodiment of the invention, when thesubstrate 101 is 127mm×127mm, the distance a' and b' from the peripheryof the substrate 101 to the pixel areas should be at least 10 mm so thatthe minimum quality of the thin films can be guaranteed. Also, thedistance a and b from the periphery of the substrate 101 to theperipheral circuit region should be at least 1.5 times larger than thedistance a' and b'. Also, the distance c and c' is preferably 5 mm orsmaller.

According to another aspect of the invention, there is provided a methodfor simultaneously manufacturing four panels that constitute respectiveliquid crystal display devices in each of which a pixel area and aperipheral driving circuit area are formed in an integral manner on asingle substrate having a insulating surface, wherein layout is so madethat the peripheral driving circuit areas of the respective panels areopposed to each other.

FIG. 3 shows a specific example of the above method, i.e., a layout forproducing four panels from one glass substrate 101. In FIG. 3, layout isso made that peripheral driving circuit areas 305 to 308 are opposed toeach other.

Where a and b are set larger than a' and b' as shown in FIG. 7, the rateof occurrence of failures in the peripheral driving circuit areas 701 to703, which have a high degree of integration and are as much prone to beaffected by particles, can be reduced. In addition, it becomes possibleto use the substrate 101 more efficiently.

Where layout is so made that the peripheral driving circuit areas 305 to308 are opposed to each other as shown in FIG. 3 in producing fourpanels from one substrate 101, occurrence of failures in the peripheraldriving circuit areas 305 to 308 can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general configuration of a panel of an active matrixliquid crystal display device incorporating peripheral driving circuits;

FIG. 2 shows a conventional layout of panels that constitute activematrix liquid crystal display devices;

FIG. 3 shows layout of panels that constitute respective active matrixdisplay devices according to a first embodiment of the presentinvention;

FIGS. 4A to 4D and FIGS. 5A to 5C are sectional views showing amanufacturing process of a panel that constitutes an active matrixliquid crystal display device according to the first embodiment;

FIG. 6 shows a layout of panels that constitute respective active matrixdisplay devices according to a second embodiment of the invention;

FIG. 7 shows a layout of panels that constitute respective active matrixdisplay devices according to a third embodiment of the invention;

FIG. 8 shows a layout of panels that constitute respective active matrixdisplay devices according to a fourth embodiment of the invention; and

FIG. 9 is a flow chart generally showing the manufacturing process ofFIGS. 4A to 4D and FIGS. 5A to 5C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 3 shows a layout of substrates which constitutes an active matrixliquid crystal display device according to this embodiment. Thisembodiment is directed to a case of allocating one glass substrate 101to four panels. In FIG. 3, reference numerals 305 to 308 denoteperipheral driving circuit areas and 301 to 304 denote pixel areas.

With the layout of FIG. 3, most part of the peripheral driving circuitareas 305 to 308, which are prone to a failure due to the existence ofparticles, can be located in regions of the substrate 101 whereparticles exist at a relatively low probability. Therefore, theoccurrence of failures due to the existence of particles can besuppressed from the case of the layout as shown in FIG. 2.

In the configuration of FIG. 3, distances a and b can be set equal toeach other. To efficiently using the substrate 101, it is preferred thatthe distances a and b be set as short as possible within a range of notreducing the yield. Since the pixel areas 301 to 304 are less likelyaffected by particles than the peripheral driving circuit areas 305 to308, the distances a and b can be set relatively short. A distance c canbe set shorter than the distances a and b.

It should be noted that where panels produced with the layout of FIG. 3include two pairs of panels having an opposite positional relationshipbetween the peripheral driving circuit area and the pixel area.

FIGS. 4A to 4D and FIGS. 5A to 5C show a manufacturing process of apanel in which a peripheral driving circuit area and a pixel area areformed on the same substrate, i.e., a panel incorporating peripheraldriving circuits. FIG. 9 is a flow chart generally showing the sameprocess.

More specifically, FIGS. 4A to 4D and FIGS. 5A to 5C shows a process ofsimultaneously forming a thin-film transistor CMOS circuit thatconstitutes a peripheral driving circuit area and N-channel thin-filmtransistors in a pixel area. Each of FIGS. 4A to 4D and FIGS. 5A to 5Cis part of a cross-section taken along line A-A' in FIG. 3.

First, a silicon oxide film 402 as an undercoat film is deposited on thesurface of a glass substrate 401 by sputtering at a thickness of 3,000Å, for instance. An amorphous silicon film 403 is deposited thereon byplasma CVD or low-pressure thermal CVD at a thickness of 500 Å, forinstance. The amorphous silicon film 403 is crystallized by illuminatingit with laser light. This results in a structure shown in FIG. 4A.Alternatively, the amorphous silicon film 403 may be crystallized byheating, or a combination of heating and laser light illumination.

By patterning the crystallized silicon film, active layers 404 and 405to constitute a CMOS circuit of the peripheral driving circuits and anactive layer 406 to constitute an N-channel thin-film transistor in thepixel area are obtained. This results in a structure shown in FIG. 4B.

Thereafter, a silicon oxide film 407 to serve as a gate insulating filmis deposited by sputtering at a thickness of 1,000 Å, for instance. Afilm mainly made of aluminum and containing a very small amount ofscandium is formed thereon by sputtering or electron beam evaporation ata thickness of 6,000 Å, for instance. By patterning the film justformed, gate electrodes 408 to 410 are formed.

Subsequently, the substrate is subjected to anodic oxidation in anelectrolyte in which the gate electrodes 408 to 410 are used as anodes,to form oxide layers 411 to 413 having a thickness of 2,000 Å, forinstance. This results in a structure shown in FIG. 4C. The oxide layers411 to 413 will become a mask in a subsequent impurity ion implantingstep, that is, will serve to form offset gate regions.

Thereafter, P+ ions (phosphorus ions) are accelerated and implanted intothe active layers 404 to 406 by ion doping or plasma doping. (FIG. 4D)

After a prescribed area is covered with a resist mask 400, B+ ions(boron ions) are accelerated and implanted by plasma doping or iondoping. (FIG. 5A)

After the resist mask 400 is removed, laser light is applied tore-crystallize the regions where impurity ions have been implanted andto activate the introduced impurity ions. (FIG. 5B)

Thus, a source region 414, a channel forming region 416, a drain region417, and offset gate regions 415 of a P-channel thin-film transistor(PTFT) 426, and a drain region 418, a channel forming region 420, asource region 421, and offset gate regions 419 of an N-channel thin-filmtransistor (NTFT) 427 are formed. The P-channel thin-film transistor 426and the N-channel thin-film transistor 427 constitute a CMOS circuit,which is part of peripheral driving circuits.

Further, a source region 422, a channel forming region 424, a drainregion 425, and offset gate regions 423 of an N-channel thin-filmtransistor (NTFT) 428 are formed at the same time as the above TFTs 426and 427.

Subsequently, a silicon oxide film as an interlayer insulating film 429is deposited by plasma CVD at a thickness of 7,000 Å, for instance.After contact holes are formed, source wiring lines 430, 432 and 433,and a drain wiring line 431 are formed with aluminum or some otherappropriate metal material. The drain wiring line 431 is common to thePTFT 426 and the NTFT 427, which constitute the CMOS circuit. Further,an ITO electrode 434 is so formed as to extend to a pixel electrode. Aprotection film 435 is then formed. Thus, as shown in FIG. 5C, theperipheral driving circuit area and the pixel area are simultaneouslyformed on the glass substrate 401.

Thereafter, the respective panels are cut out to produce individualpanels. Thus, the panels to constitute active matrix liquid crystaldisplay devices can be obtained.

Embodiment 2

This embodiment is directed to a case of producing two panels from oneglass substrate. FIG. 6 shows a general layout of this embodiment. InFIG. 6, reference numerals 603 and 604 denote peripheral driving circuitareas and numerals 601 and 602 represent pixel areas. With theconfiguration of FIG. 6, the yield of the panel formation can beincreased by making a' longer than a. That is, by making the dimensiona' long which considerably affects the rate of occurrence of failures,the reduction of the utilization ratio of a substrate 101 can beminimized as well as the yield can be made high. As for dimensions a, band b', a relationship b≈b'≈a may be established in terms of minimumnecessary values. Distance c can be set smaller than a, a', b and b'.That is, a relationship a, a', b, b'>c can be established.

While the relationships among a, a', b, b' and c are given as describedabove, specific values of these parameters depend on a necessary yield,conditions of device manufacturing process, and the cleanliness of theprocess and need to be determined experimentally.

Embodiment 3

This embodiment is directed to a case of producing four panels from oneglass substrate 101 with a layout shown in FIG. 7. In FIG. 7, referencenumerals 701 to 704 denote peripheral driving circuit areas and numerals705 to 708 represent pixel areas. With the layout of FIG. 7, the rate ofoccurrence of failures due to particles that fall on the peripheraldriving circuit areas 701 to 704 call be suppressed by establishing arelationship a'<a and b'<b. At the same time, by making a' and b' short,panels can be produced with efficient use of the glass substrate 101.Relationships a≈b and a'≈b' may be established. Distances c and c' canbe set shorter than a, a', b and b', that is, can be selected withinsuch ranges as to satisfy a relationship c, c'<a, a', b, b'. Further, arelationship c=c' may be established.

With the layout of FIG. 7, the positional relationship between theperipheral driving circuit area and the pixel area can be made identicalin any of the panels. Therefore, this layout is advantageous over thelayout of FIG. 3 in being capable of producing panels having the sameconfiguration.

Embodiment 4

This embodiment is directed to a case of producing two panels with alayout shown in FIG. 8. In FIG. 8, reference numerals 801 and 802 denoteperipheral driving circuit areas and numerals 803 and 804 representpixel areas.

With the layout of FIG. 8, the rate of occurrence of failures in theperipheral driving circuit areas 801 and 802 can be suppressed byestablishing relationships a>a' and b>b', as well as a glass substrate101 can be used efficiently. A relationship a=b may be established aslong as there is no particular problem. Similarly, a relationship a'=b'may be established as long as there is no particular problem. Distance ccan be so set as to satisfy a condition a, a', b, b'>c.

As described above, in the manufacture of the active matrix liquidcrystal display device, the invention can improve the yield whileefficiently using glass substrates.

What is claimed is:
 1. A method for simultaneously manufacturing fourpanels that constitute respective liquid crystal display devices in eachof which both a pixel area and a peripheral driving circuit area areformed in an integral manner on the same substrate having an insulatingsurface, wherein layout is so made that the peripheral driving circuitareas of the respective panels are opposed to each other and the pixelareas of the respective panels face a perimeter of the substrate.
 2. Themethod according to claim 1, wherein a distance between the peripheraldriving circuit areas is 5 mm or less.
 3. A method for manufacturing apanel that constitutes a liquid crystal display device in which both apixel area and a peripheral driving circuit area are formed in anintegral manner in the same substrate having an insulating surface,wherein layout is so made that a distance between one side of aperimeter of the substrate and the peripheral driving circuit area islonger than a distance between another side of the perimeter of thesubstrate and the pixel area, and wherein most of said one side of theperimeter of the substrate is adjacent to said peripheral drivingcircuit area and most of said another side of the perimeter of thesubstrate is adjacent to said pixel area,wherein said distance betweensaid another side of the perimeter of the substrate and said pixel areais at least 10 mm when the substrate is about 127mm×127mm.
 4. A methodfor simultaneously manufacturing a plurality of panels that constituterespective liquid crystal display devices in each of which both a pixelarea and a peripheral driving circuit area are formed in an integralmanner on the same substrate having an insulating surface, whereinlayout is so made that a distance between one side of a perimeter of thesubstrate and the peripheral driving circuit area is longer than adistance between another side of the perimeter of the substrate and thepixel area, and wherein most of said one side of the perimeter of thesubstrate is adjacent to said peripheral driving circuit area and mostof said another side of the perimeter of the substrate is adjacent tosaid pixel area,wherein said distance between said another side of theperimeter of the substrate and said pixel area is at least 10 mm whenthe substrate is about 127mm×127mm.
 5. A method for manufacturing apanel that constitutes a liquid crystal display device in which both apixel area and a peripheral driving circuit area are formed in anintegral manner in the same substrate having an insulating surface,wherein layout is so made that a distance between one side of aperimeter of the substrate and the peripheral driving circuit area islonger than a distance between another side of the perimeter of thesubstrate and the pixel area, and wherein most of said one side of theperimeter of the substrate is adjacent to said peripheral drivingcircuit area and most of said another side of the perimeter of thesubstrate is adjacent to said pixel area,wherein said distance betweensaid one side of the perimeter of the substrate and said peripheraldriving circuit areas is at least about 1.5 times greater than saiddistance between said another side of the perimeter of the substrate andthe pixel area.
 6. A method for simultaneously manufacturing a pluralityof panels that constitute respective liquid crystal display devices ineach of which both a pixel area and a peripheral driving circuit areaare formed in an integral manner on the same substrate having aninsulating surface, wherein layout is so made that a distance betweenone side of a perimeter of the substrate and the peripheral drivingcircuit area is longer than a distance between another side of theperimeter of the substrate and the pixel area, and wherein most of saidone side of the perimeter of the substrate is adjacent to saidperipheral driving circuit area and most of said another side of theperimeter of the substrate is adjacent to said pixel area,wherein saiddistance between said one side of the perimeter of the substrate andsaid peripheral driving circuit areas is at least about 1.5 timesgreater than said distance between said another side of the perimeter ofthe substrate and the pixel area.